This invention relates to electrochemical zinc-oxygen cells and more particularly to electrochemical zinc-oxygen cells which have annular electrodes wherein oxygen flows through the central portion of a diffusion cathode and a liquid electrolyte flows between the cathode a and a concentric anode spaced from the cathode. The cell of this invention may be recharged electrochemically or by replenishment of active zinc particles in the electrolyte.
Zinc-oxygen cells have been used in batteries for electric vehicles and the like because they provide high energy density relative to other gas diffusion cells, and therefore high capacity. Zinc-oxygen cells may be recharged by mechanically replacing the zinc electrode, by replacing the liquid electrolyte which contains zinc particles or by electrochemically replenishing zinc to the anode.
Many zinc-oxygen cells have a zinc anode and an oxygen cathode separated by a liquid electrolyte. Other zinc-oxygen cells have anode active zinc particles dispersed in the electrolyte and a non-chemically reactive anode. When an external electrical load is connected to the electrodes, current flows through the circuit of the cell and load due to chemical reactions which take place at the electrode surfaces.
Prior zinc-oxygen cells have not been as stable as desired due in part to the zinc anode surface becoming uneven in operation in both the discharge and the electrochemical charge mode. Further, zincate ions formed in the electrolyte may decrease the electrocatalytic activity of the electrocatalytically active gas-electrolyte-electrode reaction sites. It is important to retain as many as possible electrocatalytically active gas-electrolyte-catalyst reaction sites readily available to each of the three phases of reaction participants.
U.S. Pat. No. 4,009,320 teaches an air-zinc battery having air passages through an active carbon cathode which is surrounded by a gelled electrolyte. U.S. Pat. No. 4,137,371 describes a zinc-oxygen cell having a zinc electrode, and an oxygen porous diffusion cathode with a diffusion of zincate restricting membrane joined directly to the oxygen electrode between the porous layer of this electrode and the zinc electrode. This is stated to prevent poisoning of the electrochemically active material by zincate ions. Flowing electrolytes containing anode active metal, such as zinc, in zinc-oxygen cells, are described in U.S. Pat. No. 4,136,232. Problems of such cells connected in series are pointed out in that patent.
None of the prior art known to the inventor suggests an electrochemical zinc-oxygen cell having concentric electrodes and a flowing electrolyte in the annular space therebetween providing slurry and electrochemical recharging in the same cell, uniform anodic deposition and an anode having greater surface area than the cathode to the electrolyte.
Accordingly, an object of this invention is to provide an electrochemical zinc-oxygen cell overcoming many of the disadvantages of prior zinc-oxygen electrochemical cells.
Another object is to provide a zinc-oxygen electrochemical cell which is of annular construction, having concentric tubular electrodes with oxygen containing gas passing through the central portion of a tubular oxygen diffusion cathode and liquid electrolyte passing through an annular space between the tubular cathode and a tubular metal anode.
Still another object is to provide a zinc-oxygen electrochemical cell having a zinc anode surface which provides more even contact with the active electrolyte and a more even surface upon repeated electrochemical recharge.
Yet another object is to provide a zinc-oxygen electrochemical cell having an anode active zinc particle-electrolyte slurry which circulates in the annular electrolyte space and may be readily replenished exterior to the cell.
Another object is to provide a zinc-oxygen electrochemical cell having a geometry permitting higher pressure differentials across the oxygen diffusion cathode structure reducing poisoning of the catalytically active reaction sites.